Emergency numbers for mobile stations are not globally unique and vary from country to country. Examples of valid emergency numbers include 911, *911 and #911 in North America, 112 and 119 in South Korea, 111 in New Zealand, 000 and 106 in Australia, 110, 119 and 112 in China, among others.
In many mobile devices, emergency numbers may be automatically dialled by selecting an emergency call feature from a menu. Typically, a carrier specifies the valid emergency numbers that a mobile device must be programmed with at the factory. For example, in North America, carriers generally program the mobile device to include 911, #911 and *911 as the emergency numbers. This is required since mobile station treats valid emergency numbers differently than other numbers. If the mobile station recognizes a dialed number as one of the emergency numbers, then it executes a special network determination algorithm to a acquire a network even if it is not preferred or even if the mobile station does not have a valid SIM or equivalent network configuration information.
Some carriers may add other numbers in anticipation of roaming in other countries. Alternatively, other numbers could be meant for specific types of emergency services such as emergency text telephony for the deaf (known as TTY).
The expectation from carriers is that a user will know the emergency number of the country that they are in and manually dial that number. This is, however, inconvenient and potentially dangerous when a user is roaming in a country that he or she may not know the emergency number in. Further, when a mobile device or the keypad is locked, a user typically cannot manually dial an emergency number without manually unlocking it first and the only option is to select an emergency call item from a menu if the menu option is available on the mobile station. In this case, mobile station typically chooses a number from the list of valid emergency numbers. In some cases, the dialed number may not be the appropriate emergency number in the geographical area when the call is placed.
Some prior art solutions have attempted to address the above difficulty in part. For example, UK Patent Application GB 2,360,176 to Charbonnier teaches a method and system in which a mobile station automatically senses when an emergency number has been dialled and captures that call. The emergency block then automatically decamps from the network that the user is currently on and connects to an overlaid emergency network. Alternatively, if an emergency network is not available, the application teaches connecting to an emergency number on the public network the user is already connected to.
The problem with the Chabonnier solution is that it does not consider geographic location and is merely directed to facilitating the emergency call completion on either an emergency network by decamping automatically and then camping onto the overlaid emergency network, or by dialling a number on the public network if an emergency network is not available.